This application is based on and claims the benefit of German Patent Application No. 19961237.4 filed Dec. 18, 1999, which is incorporated by reference herein.
The invention relates to an antenna for radiating and receiving electromagnetic waves. Such an antenna comprises a parabolic reflector, and an exciter which is designed as a sub-reflector and which is attached in the focal point of the reflector at the end of a waveguide, guided through the center of the reflector. On the backside of the reflector a radio box containing electric and electronic components is attached to the waveguide, which is connected to a transmitter-receiver, e.g., as disclosed in German published application DE 197 25 047 A1.
Such antennas are called xe2x80x9cCassegrainxe2x80x9d antennas due to the sub-reflector. They are used, for example, for mobile radio applications. The construction of antennas, according to the aforementioned German published application DE 197 25 047 A1, is relatively simple, since the horn, serving as the xe2x80x9cexciter,xe2x80x9d and the sub-reflector are carried by waveguides, attached in the center of the reflector. The waveguide projects beyond the reflector, and on the backside there is a radio box, which is attached to the waveguide. Starting from the radio box, a coaxial high frequency cable runs to a transmitter-receiver. The radio box accommodates the electric and electronic components and a transmission path for the electromagnetic waves. This prior art antenna is designed to transmit a linearly polarized wave of a frequency or a frequency band.
The invention is directed to the problem of improving the transmission capacity of such an antenna without significantly changing its construction.
The invention solves this problem by providing a polarization diplexer between the radio box and the waveguide for simultaneous transmission of two orthogonal, linearly polarized waves, the diplexer having first and second inputs with an essentially rectangular clear cross section and an output, which can be attached to the waveguide, and by providing the polarization diplexer with two waveguide segments, of which the one runs linearly between the first input and the output of the polarization diplexer, whereas the other, starting as a 90xc2x0 curve at the second input of the polarization diplexer, empties into the linear waveguide segment in the course of the linear waveguide segment, with the linear waveguide segment being rotated by 90xc2x0 in the input area so that the large axes of the two inputs of the polarization diplexer that lie in the same plane are at right angles to each other.
By incorporating the polarization diplexer, the antenna can be used to transmit two separate, electromagnetic waves without having to change its basic design. In this manner the transmission capacity of the antenna is doubled in a simple manner. At the same time the polarization diplexer, whose dimensions are small, can be provided in place of the conventional simple waveguide segment so that the radio box can remain unaltered, except for an adapted xe2x80x9cinternal life.xe2x80x9d Therefore, no modifications have to be made in order to install the radio box at the reflector of the antenna. Hence, the polarization diplexer replaces a waveguide segment, which was used in the past to connect to the waveguide of the antenna. The attachment of the radio box to the polarization diplexer is also very simple, since the two inputs of the same lie in one plane. The decoupling of the two linearly polarized waves is guaranteed in a simple manner in that the large axes of the two inputs of the polarization diplexer run at right angles to each other.